Production of flexible sheet materials



May 23, 1967 P. MERRIMAN ETAL 3,

PRODUCTION OF FLEXIBLE SHEET MATERIALS 7 Filed July 10, 1964 E m MMMW wflmR mawdfm Z 3. 5 M m 3 P. p Y B United States Patent 3,321,356 PRODUCTION OF FLEmLE SHEET MATERIALS Peter Merriman, Edgbaston, and Dennis Ivor Clarke, Birmingham, England, assignors to Dunlop Rubber Company Limited, London, England, a British company Filed July 10, 1964, Ser. No. 381,876 Claims priority, application Great Britain, July 31, 1963,

30,289/ 63 Claims. (Cl. 161-81) This invention relates to the production of flexible sheet materials comprising fibrous material and a flexible binder, including sheet materials intended to form a substitute for natural leather, and also sheet materials intended for the manufacture of belting, diaphragms, filters, and so forth. It is an object of the present invention to provide for differential distribution of the binder in the transverse sense, i.e. to enable the concentration of binder to be made greater at and near one surface of the material than it is at and near the other surface.

According to the present invention, a method of producing flexible sheet material comprises preparing a layer of fibrous material, applying to the layer a liquid comprising a binder and a vaporisable vehicle, and securing diflerential distribution of binder by applying heat to one surface of the layer differentially with respect to the other surface, removal of the vehicle by vapon'sation and (if appropriate) heat-curing of the binder being also effected by the application of heat. The differential heating just specified has been found to induce migration of binder away from the relatively cool surface and towards the relatively hot surface, and it is believed that this migration may result from a progressive rinsing of the binder from one surface to the other by the liquid phase of the vehicle, some of which is assumed to condense towards the relatively cool surface after being vaporised towards the relatively hot surface.

Normally it is desirable that the layer of fibrous mate rial, with the liquid comprising the binder and vaporisable vehicle, should be confined and compressed between metal or other plates (or belts, if production is to be continuous) while the differential heating is performed. Generally it is appropriate to heat positively one of the plates (or belts) and to leave the other unheated, or to apply positive cooling, though it should be understood that according to the nature of the binder used, the nature of the product desired, and so forth, the differential heating may if necessary be supplemented by substantially uniform heating of the material under treatment when once the differential distribution of the binder has been provided for. Spacers may be used between the plates (or belts) to prevent excessive compression of the material under treatment, and also the edges of the plates (or belts) may be enclosed with a view to preventing excessively rapid escape of the vaporisable vehicle. As will be appreciated, the temperature of the hotter plate (or belt) in the differential heating should be high enough to vaporise this vehicle; the hotter plate (or belt) in the differential heating may also supply all the heat needed for any heat-curing of the binder, so as to avoid supplementary heating.

The liquid comprising a binder and a vaporisable vehicle may be a solution, e.g. a solution of a polyurethane rubber or intermediate chemical system reacting to form such a rubber in acetone or another organic solvent, or a dispersion, e.g. a rubber latex or an aqueous emulsion of a solution of an elastomer in an organic solvent. It

must be understood, however, that before or after the differential distribution of binder present in this liquid has been secured, a supplementary binder (e.g. a compounded rubber latex) may be applied if desired, and

3,321,356 Patented May 23, 1967 that surface finishing coating (e.g. of a polyurethane lacquer) may also be applied if desired.

The layer of fibrous material used may take any of a variety of forms. It may for instance be in the nature of a felt, or a fleece. A specific example of the fibrous material layers which may be used is that comprising a web of interpenetrated crimped continuous nylon monofilaments which after needle-punching has been overlaid with a fleece of polypropylene staple fibres, the latter having been needle-punched beforehand and also after being laid on the nylon web. Particularly good results are obtainable if the binder-rich part of the product is derived from fine-denier fibres, egg. by laying one or more fine-denier fleeces on a coarser base web and if desired uniting them by needle-punching. This assists the migration of the binder and promotes continuity and fine poros ity in the binder-rich surface.

By the differential-heating technique of the present invention, it is possible to obtain flexible sheet materials having a smooth, cfinely porous surface of binder on one side and a surface with much less or no binder on the other side. We have found that the present technique has (in the field for which it is intended) substantial advantages over the other techniques for differentially distributing the binder which we have considered; these other techniques were (1) surface application of binder, which was liable to give a rough surface or alternatively a readily detached non-porous stratum, (2) surface accumulation by pressing, which was liable to give undifferentiated ob verse and reverse surfaces, (3) gravitation to a lowermost surface, which was liable to give a non-porous surface layer and which in any case required an open fibrous layer and a high proportion of binder, and (4) capillary migration, which was liable to give a rough and uneven surface.

The invention will now be illustrated by way of example only with reference to the accompanying drawing, in which- FIGURE 1 is a cross-sectional view of a mat of fibres prior to impregnation with a binder;

FIGURE 2 is a cross-sectional view of the' mat subsequent to impregnation with a binder and after differential distribution of the binder;

FIGURE 2A is an enlarged view of the uppermost layer of the mat shown in FIGURE 2; and

FIGURE 3 is a cross-sectional view of the mat subsequent to impregnation with a second binder.

Referring now to the drawing, FIGURE 1 shows a cross-section through a mat 1 formed from a layer of crimped continuous nylon filaments 2 and a layer of polypropylene staple fibres 3. The mat 1 is made by laying a needle-punched mat of the staple fibres 3 on the layer of continuous filaments 2 and needlingthe assembled layers together.

FIGURE 2 shows a cross-section through the mat after the mat has been impregnated with a polyurethane binder composition 5, and after differential distribution of this binder composition. The polypropylene staple fibre layer contains the major proportion of the binder composition and the layer of staple fibres and binder is shown by the reference numeral 4 in FIGURE 2. The polypropylene fibres 3 are embedded in the binder 5 as shown in the enlarged cross-section through the layer 4 in FIGURE 2A. The layer 4 also contains small air-spaces 6.

The mat shown in FIGURE 3 contains a rubber composition (second binder composition) 7 which is applied to the mat shown in FIGURES 2 and 2A and is then cured. As shown in FIGURE 3, the rubber composition 7 penetrates the polyurethane layer 4 and fills the airspaces 6 of this layer.

The following examples illustrate'the invention.

3 Example I A web of crimped continuous 6-denier nylon 66 monofilaments, laid under light tension in the form of parallel continuous yarns and subsequently relaxed, and which weighed approximately 20 grams per sq. ft. in the relaxed condition, was passed once through a needle-punching machine and then covered with a fleece of randomly oriented 3-denier polypropylene fibre of 2 /2" staple length which had previously been needle-punched and weighed approximately 6 grams per sq. ft. The assembly was then needled a further 4 times. A one foot square of the resulting composite felt weighing 24 grams was laid, nylon side downwards, on a steel plate covered With a polyethylene foil. 50 grams of a freshly prepared solution containing 96 parts by weight of the liquid polyurethane rubber Adiprene L-100, 4 parts of trimethylolpropane and 1 part of stannous octoate in 100 parts of dry acetone, were poured centrally on to the top surface of the felt, into which the whole of it soaked and to some extent spread out.

The top surface was immediately covered with a sheet of polyethylene foil and then another steel plate. The assembly was placed in a cold platen press and compressed without spacers under a pressure of 230 lbs.-/ sq. in. for 75 seconds to distribute the solution uniformly. About 10 grams of the solution extruded at the edges and was not recovered. The press was then opened and the felt removed. At this stage it was a completely wetted open structure about 4 mm. thick. It was immediately laid, polypropylene fibre side upwards, between two polypropylene sheets and placed in a mould fitted with spacers to give a depth of 1 /2 mm. between the polypropylene sheets.

This assembly was placed in a press having the bottom platen at room temperature and the top platen at 100 C., and pressed to 230 lbs/sq. in. After ten minutes the temperature of both platens was raised to 110 C. and pressing continued at this temperature for a further ten minutes. The press was then cooled and opened and the product removed. It consisted of a 2 mm. thick sheet having a supple feel and a smooth finely porous top surface consisting of compacted polypropylene fibres embedded in porous elastomeric polyurethane, the reverse (nylon fibre) surface of the sheet being denuded of polyurethane.

This product had a tensile strength of 750 lbs./sq. in. and an elongation at break figure of 85%. After applying a polyurethane lacquer finish to the top surface it had a very leather-like appearance, and after impregnation with 50 grams dry weight of rubber latex and 'bufiing the back surface, a very leather-like product was obtained having a tensile strength of over 2000 lbs./sq. in., an elongation at break figure of over 80%, a flex life greater than 1 million cycles on the standard (SATRA) vamp-flexing machine, and a water-vapour permeability of 0.43 mg./sq. cm./hr. It conformed also with other typical natural leather test specifications.

Example 11 The procedure of Example I was repeated except that the composite web employed consisted of grams per sq. ft. of continuous nylon 66, 5 grams per sq. ft. of 3-denier polypropylene staple and a top layer of 5 grams per sq. ft. of lVz-denier nylon 66 staple.

The product was very similar to that of Example I and after impregnation and coating had a flex life of over 3.8 million cycles.

Example III A felt was prepared, impregnated and pressed exactly as in Example II except that the spacers were adjusted to compress the product to 1.0 mm.

The top surface of the product was of the same character as before, but the back surface, although of an open fibrous texture, retained sufficient polyurethane for the material to serve as an artificial leather without any further impregnation treatment.

Example IV The procedure of Example I was repeated exactly except that the random fleece of polypropylene was replaced by two laps of PAM-denier, high-crimp, 1 /2"-staple nylon 66, each weighing 3.5 grams/sq. ft. The first of these laps was laid with its principal fibre direction crossing the underlying nylon yarns at an angle of 45 and the second was laid at to the first, i.e. also crossing the underlying yarns at 45 but inclined in the opposite direction.

The product obtained after impregnation with rubber latex and bufiing the back surface was similar in appearance to the corresponding product of Example I and gave the following test data:

Direction of measurement Sample 1.4 mm. thick Stitch tear (lb./in.) 710 590 Tongue tear (lb/in.)

Example V A web was prepared as in Example I and laid as before on a steel plate covered with a polyethylene foil. 60 grams of a freshly prepared compounded ammonia-preserved natural rubber latex mix of the following composition was poured centrally on to the top of the felt:

Parts by weight Natural rubber latex (60% dry rubber content) 100.0 Aqueous solution of potassium oleate (15 g./ g.

solution) 6.7 Aqueous dispersion of sulphur (50 g./ 100 g. dispersion) 2.0 Aqueous dispersion of dibetanaphthyl-p-phenylene diamine (40 g./ 100 g. dispersion) 2.5 Aqueous dispersion of zinc diethyldithiocarbamate (5O g./100 g. dispersion) 1.0 Aqueous dispersion of zinc salt of mercaptobenzothiazole (50 g./ 100 g. dispersion) 3.0 Water 54.0 Aqueous dispersion of zinc oxide (50 g./ 100 g.

dispersion) added just before use 6.0

The latex mix soaked into the web and to some extent spread out.

The top surface was immediately covered with a sheet of polyethylene foil and then another steel plate. The assembly was placed in the press and compressed without spacers at 230 lb./sq. in. for 30 seconds. About 15 grams of the latex mix extruded at the edges and was not recovered. The press was opened and the felt removed. At this stage it was a completely wetted, open structure about 4 mm. thick. It was immediately laid, polypropylene fibre side upwards, between two polypropylene sheets and placed in a mould fitted with spacers to give a depth of 1.5 mm.

The assembly was pressed at 230 lb./sq. in. with the bottom platen initially att about 40 C. and the top platen at C. After 20 minutes the temperature of the bottom platen had gradually increased to about 80 C., the top platen temperature remaining at 130 C. The press was then cooled and opened, and the product removed. It consisted of a fully dried and cured 1.5 mm. thick sheet. It had an extremely supple feel and a smooth finely porous top surface consisting of polypropylene fibres embedded in a porous vulcanized latex rubber, the reverse (nylon fibre) surface of the sheet being denuded of rubber and having acquired an attractively smooth surface by heat setting in the presence of the steam from the latex evaporation. dicate sufliciently high-level properties to yield a good leather replacement material after a supplementary and more uniform impregnation with a further quantity of binder applied from the back.

A web of the crimped continuous 6-denier nylon 66 monofil was relaxed as before and then needle-punched 6 times from alternate sides. It then weighed 19 grams per sq. ft.

An emulsion of a liquid polyurethane rubber (Adiprene 11-100) was prepared as follows. 100 parts of Adiprene L-lOO were dissolved in 50 parts of toluene and then 4 parts of the addition product of ethylene oxide and nonylphenol sold under the trade name of Nonidet P-40 were stirred in. Separately, the following ingredients were mixed with 66 parts of water: 30 parts of a solution in 90 parts of water of 10 parts of sodium dodecyl sulphate, 20 parts of a solution in 95 parts of water of 5 parts of dioctyl sodium sulphosuccinate sold under the trade name Manoxol N, and 30 parts of an aqueous solution of ammonium caseinate made by dissolving in 990 parts of water 100 parts of lactic casein, 1 part of sodium pentachlorophenate and 9 parts of aqueous ammonia solution of specific gravity 0.880. The above Adiprene solution was slowly poured with high-speed stirring into the aqueous liquid, yielding an oil-in-water-type emulsion which remained colloidally stable for many weeks. The fieshly prepared emulsion was matured at room temperature for 24 hours by which time test films dried at room temperature on a glass plate consisted of coherent, substantially tack-free elastomer.

The nylon web (1 sq. ft.) was treated with 50 grams of this matured emulsion and then given the same subsequent treatment as the web in Example V. (The extrusion loss in the first pressing was 14 grams of emulsion.)

The product after the second pressing was a fully dried and cured 1.5 mm.-thick strong flexible sheet having a smooth finely porous top surface and a smooth open back surface devoid of Adiprene.

Example VII A 1 ft. square nylon web similar to that in Example VI but weighing 23 grams was first impregnated substantially uniformly throughout its thickness with Adiprene binder by the following technique. 50 grams of a freshly prepared solution of 96 parts of Adiprene, 4 parts of trimethylolpropane and 1 part of stannous octoate, all dissolved in 400 parts of dry acetone, were poured on centrally, and the cold pressing applied as before. This caused the extrusion of 20 grams of the solution. On release, the remaining 30 grams of solution were found to be almost evenly distributed throughout the web. The web was immediately transferred to a well-ventilated hotair oven at 80 C. for 5 minutes, by the end of which time the acetone had substantially all evaporated before any appreciable drainage of solution had had time to occur. At this stage the Adiprene was weak and tacky. The web was then pressed to 1.5 mm. for 15 minutes in a press having both its platens at 100 C., yielding a fully cured 1.5 mm. thick sheet.

It gave the following test data which inp solution and technique described in Example I. No excess solution exuded in the cold pressing and the web, already 1.5 mm. thick in the wet state, was held at 1.5 mm. during the hot pressing.

The final product was a leather-like sheet having a strongly increasing graduation of Adiprene binder content from the bottom to the top surface, and this top surface had the smooth and finely porous quality characteristic of the invention.

Having now described our invention, what we claim is:

1. A method of producing flexible sheet material which comprises distributing throughout a layer of fibrous material, a liquid comprising a binder for the fibres of said fibrous material and a vaporisable vehicle for said binder and applying heat to one surface of said layer to raise its temperature adjacent this surface above the tempera ture adjacent to the other surface to secure a differential distribution and a concentration of said binder adjacent said heated surface to remove the vehicle by vaporization and to heat-cure said binder.

2. A method according to claim 1, in which the layer of fibrous material incorporating the liquid comprising the binder and vaporisable vehicle, is confined and compressed between plates while the differential heating is performed.

3. A method according to claim 2, in which one of the plates is heated positively and the other is left unheated.

4. A method according to claim 2 in which one of the plates is heated positively and the other is cooled positively.

5. A method according to claim 4 using a solution of an intermediate chemical system reacting to form a polyurethane rubber in an organic solvent.

6. A method according to claim 1, in which the liquid comprising a binder and a vaporisable vehicle is a solution.

7. A method according to claim 5, using a solution of a polyurethane rubber in an organic solvent.

8. A method according to claim 1, in which the liquid comprising a binder and a vaporisable vehicle is a rubber latex.

9. A method according to claim 1 in which a supplementary binder is applied after applying said liquid.

10. A method according to claim 9 in which the supplementary binder is a compounded rubber latex.

11. A method according to claim 1 in which the layer of fibrous material incorporating the liquid comprising the binder and vaporisable vehicle, is confined and compressed between belts while the differential heating is performed in a continuous process.

12. A method according to claim 11 in which one of the belts is heated positively and the other is left unheated.

13. A method according to claim 11 in which one of the belts is heated positively and the other is cooled positively.

14. A method according to claim 1 in which the layer of fibrous material comprises a web of needle-punched interpenetrated crimp continuous nylon monofilaments overlaid with a fleece of needle-punched polypropylene staple fibres and needle-punched on the nylon web.

15. A method according to claim 1 in which the liquid comprises a binder and a vaporisable vehicle is an aqueous emulsion of a solution of an elastomer in an organic solvent.

16. Flexible sheet material which comprises a layer of matted fibrous material and a flexible binder for said fibres differentially distributed throughout said layer, the concentration of said binder being greater adjacent to one surface of said layer than adjacent the other surface of said layer.

17. The flexible sheet material of claim 16 in which said material'has a smooth, finely porous surface of compacted fibres and binder.

18. The flexible sheet material of claim 16 in which said layer of matted fibrous material comprises a layer of interpenetrated continuous monofilaments and a layer superposed on the above layer of randomly oriented fibres, and in which said concentration of binder is greatest in said superposed layer.

19. The flexible sheet material of claim 18 in which said continuous monofilaments are nylon and said 10 randomly oriented fibres are polyethylene.

20. The flexible material of claim 18 in which said layers of continuous interpenetrated continuous monofilaments and randomly oriented fibres have been united by needle-punching.

References Cited by the Examiner UNITED STATES PATENTS 2,970,365 2/ 1961 Morgenstern 28--72.2 X 2,994,940 8/1961 Ferrell et a1 38-74 X 3,141,809 7/1964 Maio et a1. 161-155 X MERVIN STEIN, Primary Examiner.

L. K. RIMRODT, Assistant Examiner. 

16. FLEXIBLE SHEET MATERIAL WHICH COMPRISES A LAYER OF MATTED FIBROUS MATERIAL AND A FLEXIBLE BINDER FOR SAID FIBRES DIFFERENTIALLY DISTRIBUTED THROUGHOUT SAID LAYER, THE CONCENTRATION OF SAID BINDER BEING GREATER ADJACENT TO ONE SURFACE OF SAID LAYER THEN ADJACENT THE OTHER SURFACE OF SAID LAYER. 